This project is based on the general hypothesis that the mechanism of cellular senescence is, in part at least, dependent on altered gene expression. We have prepared RNA stocks from young and senescent cells at seven time points. We have worked extensively with the G0 time point (i.e. unstimulated cells) and identified by screening eleven genes that are differentially expressed. We plan now to characterize four of these extensively. Two of them, EPC-1 and EPC-A2 are overexpressed in young cells; LPC-1 is overexpressed in senescent cells and its expression is uncoupled from the cell cycle. The fourth is the mitochondrial electron transport system genes. These are overexpressed in senescent cells. We plan to characterize the regulation and physiologic significance of altered regulation of these genes. In addition, we will compare the alterations resulting from aging in vitro with possible changes in early passage skin fibroblasts from people of different ages. Finally, as time permits, we will identify and characterize additional differentially expressed genes.